The present invention relates to caging systems for housing and isolating laboratory animals, and in particular to cage assemblies for the breeding of colonies of mice, rats or other small laboratory animals or for laboratory experimental work with such animals. Each of the cage assemblies includes a see-through cap or bonnet which has a detachable reusable filter, and remains securely in place on the cage body without being fastened thereto, to function as an effective microbiological barrier.
In the production of colonies of mice or other small laboratory animals by breeding, the mice are housed in animal cages which are arranged in close proximity within confined areas. The colonies are subject to air-borne diseases which spread rapidly from one cage to another, particularly where the surrounding environment is not particularly sanitary. It is particularly desirable to maintain a closed, limited Defined Flora colony, that is a colony of mice having a limited number of bacteria which are constantly the same. It has hitherto been impossible to maintain a constant flora over long periods of time without employing complex isolator systems which are expensive and not economically feasible in the breeding production of laboratory mice.
The same problems are encountered in the maintenance of the animals during laboratory experimental work. Although the surrounding environment is more sanitary, the animals are housed in open cages which are arranged to close proximity to each other, usually, on multi-tier racks. The animals in the different cages may be infected with various selected diseases while others may be uninfected for comparison purposes. It has been difficult or impossible to prevent the spread of diseases from one cage to another without employing complex isolator systems.
Conventional cages for small laboratory animals are usually of the open-mesh type in which the cage side and bottom walls are made of wire grill or perforated metal, or of the "shoe-box" type having solid imperforate side and bottom walls made of transparent plastic material, and an open top. The cage assembly of the invention herein is directed to the latter type of "shoe-box" transparent cage body, in combination with a filter cover therefor. The cage body may include a removable lid made of a grid of straight spaced bars, and shaped to contain hoppers for the storage of food and water which are easily accessible to the animals within the cage. The term "cage", as used in this description, generally refers to a cage body or tray having solid side and bottom walls and an open top, with the optional inclusion of a grid-type lid overlaying the open top and having means for mounting water and food containers.
In the use of such cages for animal production or experimental laboratory research, it is imperative that bacteriological conditions established in an individual cage be maintained for as long as such conditions are desired. It is also desirable to have a clear view of the animals through any top cover provided for the cage, since other portions of the cage are occasionally obstructed.
In my aforementioned prior patent application Ser. No. 422,355 there is shown an animal cage filter cap which is constructed to be removably mounted in secure position upon standard animal cages having transparent walls, and which provides with the cage an effective microbacterial barrier for the animals housed therein, and minimize the emission of odors from the cage by maintaining limited defined anaerobic bacterial flora. The filter cap is reusable and mounts a removable and reusable filter, both the cap body and filter being capable of being autoclaved. The filter cap is transparent so that the housed animals may be observed therethrough, and is in the shape of a box-like enclosure sized to fit upon the open top end of the animal cage in overlapping relationship with the cage wall. The filter cap has a resting surface which is formed to engage a corresponding surface portion of the cage to effect a substantial seal like a petri dish between the cap and the cage.
The cage cap of my aforementioned patent application Ser. No. 422,355 includes an autoclavable filter in the form of a thin sheet which overlies the open top end of the cap body and which admits filtered air into the enclosed assembly. The filter is detachably mounted on the cage cap so that it may be removed when necessary for separate sterilization or for replacement. The filter is covered over by a perforated metal plate which protects the filter from damage during handling of the cage cap, and the metal plate and underlying filter are attached to the cap by bolts and nuts.
The animal cage filter cap of the present invention is identical in general structure and function to the filter cap described above and provides all of the aforementioned advantages. It includes, however, improved means for detachably mounting the filter on the cap body. The perforated metal plate and the bolts and nuts are replaced by an integral perforated top wall on the cage body, and a plastic retainer member detachably secures the filter in mounted position upon the cap body by a snap fit, with the filter sandwiched between the perforated top wall and the retainer member.
It is the principal object of the present invention to provide an animal cage filter cap of the character described which includes novel means for mounting the filter on the cap body so that the filter can be quickly removed and replaced, minimizing the time in which the animals within the cage are exposed to an unfiltered environment.
Another object of the invention is the provision of an animal cage filter cap of the character described which is rigid, durable, inexpensive to produce, easy to sterilize for reuse, easy to handle, uses minimal rack space, does not dislodge when adjacently-disposed cages are pushed against one another, and allows easy access to selected cages without time-consuming entry procedures.